Polyetherimide oligomer

ABSTRACT

Polyetherimide oligomers having crosslinking end cap moieties which provide improved solvent-resistance to cured composites are generally represented by the formula: ##STR1## wherein X=--O-- or --S--; ##STR2## n=1 or 2; ##STR3## E=allyl or methallyl; R=a trivalent C 6-13 ) aromatic organic radical; 
     R 1  =any of lower alkyl, lower alkoxy, aryl, or substituted aryl; 
     R&#39;=a divalent C 6-30 ) aromatic organic radical; 
     j=0, 1, or 2; and 
     G=--CH 2  --, --O--, --S--, or --SO 2  -- 
     Blends generally comprise substantially equimolar amounts of the oligomers and a comparable, compatible, noncrosslinking, etherimide polymer of substantially the same backbone. The crosslinkable oligomers are made by reacting substituted phthalic anhydrides with hydroxyaryl amines and suitable crosslinking end cap reactants, or by self-condensation of phthalimide salts followed by capping the polymers. Related polyetherimides of the present invention can be prepared by the condensation of nitrophthalic anhydride, diamines, dialcohols (dihydricphenols), and phenolic, crosslinking end caps (A-OH), or the condensation of bis(phenates) or dialcohols (bisphenols), diamines, nitrophthalic anhydride, and amine-terminated end caps (A-NH 2 ) or nitro-terminated end caps (A-NO 2 ). 
     The oligomers and blends can be prepregged, and can be cured to form advanced composites having aerospace applications.

TECHNICAL FIELD

The present invention relates to polyetherimide oligomers that arecurable into high performance composites and to their method ofmanufacture. The oligomers have crosslinking end cap functionalitieswhich improve the solvent-resistance of the composites. Blends of theoligomers and polymers are also described.

BACKGROUND ART

Polyetherimides can be prepared by the self-condensation of hydroxyarylphthalimide salts, as disclosed in U.S. Pat. No. 4,297,474 (which isincorporated by reference into this description). The polymers have thegeneral formula: ##STR4## wherein R is a trivalent C.sub.(6-13) aromaticorganic radical, R' is a divalent C.sub.(6-30) aromatic organic radical,and X is --O-- or --S--. The polymers have alternating imide and ether(or thioether) linkages between aromatic radicals. Similarpolyetherimide polymers are prepared by the reaction of alkali metaldihydric phenol and an organic bis(fluorophthalimide) in the presence ofa dipolar aprotic solvent, as disclosed in U.S. Pat. No. 3,847,869(which also is incorporated by reference into this description).Polysulfoneimides of the same general type are prepared by the reactionof an aromatic bis(sulfoneanhydride) with an organic diamine, asdisclosed in U.S. Pat. No. 4,107,147 (which also is incorporated byreference into this description). While these etherimide andsulfoneimide polymers are suitable for films, coatings, etc., theirsolvent-resistance and other physical properties in composite form canbe improved by adding crosslinking end cap functionalities to thepolymer backbones, thereby making the composites (cured from theoligomers) better suited for high performance applications, such asaerospace needs.

SUMMARY OF THE INVENTION

Polyetherimide (or sulfoneimides) oligomers of the present inventionhave the general formula: ##STR5## wherein X =--O-- or --S--; ##STR6##n=1 or 2; ##STR7## E=allyl or methallyl; R=a trivalent C.sub.(6-13)aromatic organic radical;

R₁ =any of lower alkyl, lower alkoxy, aryl, or substituted aryl(including hydroxyl or halo substituents);

R'=a divalent C.sub.(6-30) aromatic organic radical;

j=0, 1, or 2; and

G=--CH₂ --, --O--, --S--, or --SO₂ --.

These oligomers can be prepared by condensing: ##STR8## ps in the ratioof I:II:III:IV=1:1:m:m wherein m=an integer greater than or equal toone, and A, R, R', and X are as defined previously, and wherein Y=halo-or nitro-. This reaction occurs in a suitable solvent under an inertatmosphere.

Compounds of the formula (I) and (II) are novel compositions of matter.Those of formula (I) can be prepared by reacting A-XH with a substitutedphthalic anhydride of the formula: ##STR9## wherein A, Y, and R are aspreviously defined. Carried out in a suitable solvent substantially tocompletion by mixing substantially equimolar amounts of the reactants,the anhydride need not be recovered, but rather the product mixture canbe added to the reaction mixture of the condensation reaction of theoligomer, if the solvents are compatible.

Compounds of formula (II) are prepared by reacting A-NH₂ with thesubstituted phthalic anhydride of formula (V). Again, the reactionproduct need not be separated from the reaction mixture to carry out theoligomer's condensation, if the solvents are compatible.

Blended compositions, preferably having substantially equimolar amountsof the oligomers and a compatible polymer, are also contemplated. Theseblends generally comprise one of the crosslinkable oligomers previouslydescribed and a noncrosslinking polymer of the type described in U.S.Pat. No. 4,297,474 that has substantially the same backbone as theoligomer. Such a polymer, however, does not possess crosslinkingcapability.

Polysulfoneimide oligomers of the present invention can be prepared byreacting:

n+1 moles of a dianhydride;

n moles of a diamine; and

2 moles of an amine end cap,

wherein the dianhydride and diamine are selected to form a polysulfoneimide backbone of the following general formula: ##STR10## wherein R andR' are divalent aromatic organic radicals having from 2-20 carbon atoms.These radicals include halogenated aromatic C.sub.(6-20) hydrocarbonderivatives; alkylene radicals and cycloalkylene radicals having from2-20 carbon atoms; C.sub.(2-8) alkylene terminatedpolydiorganosiloxanes; and radicals of the formula: ##STR11## whereq=--C_(y) H_(2y) --, --CO--, --SO₂ --, --O--, or --S--; and y=1 to 5.

Oligomers of the present invention can also be prepared by thecondensation of nitrophthalic anhydride, diamines, dialcohols, andphenolic end caps.

Prepregs and composites of these oligomers and blends can also be made.

BEST MODE CONTEMPLATED FOR CARRYING OUT THE INVENTION

Polyetherimides and polysulfoneimides are capped with mono- anddifunctional, crosslinking phenylimides to produce oligomers that arecurable to composites which exhibit improved solvent resistance. The endcap phenylimides can be selected to provide cure and use temperatureswithin a relatively wide range.

Preferred compounds have the general formula: ##STR12## wherein X=--O--or --S--; ##STR13## n=1 or 2; ##STR14## E=allyl or methallyl; R=atrivalent C.sub.(6-13) aromatic organic radical;

R₁ =any of lower alkyl, lower alkoxy, aryl, or substituted aryl(including hydroxyl or halo substituents);

R'=a divalent C.sub.(6-30) aromatic organic radical;

j=0, 1, or 2; and

G=--CH₂ --, --O--, --S--, or --SO₂ --.

The crosslinking end caps radicals (A) are readily prepared by thecondensation of the corresponding anhydride and a suitable amine, asdescribed in U. S. Pat. No. 4,604,437 with respect to theallyl-substituted or methallyl-substitutedmethylbicyclo[2.2.1]hept-5-ene-2,3-dicarboximides.

The end cap radicals are unsaturated, substituted phenylimides, and aregenerally selected from the group consisting of: ##STR15## wherein n=1or 2 ##STR16## and R¹, G, j are as previously defined. The mostpreferred end caps (to provide the highest thermal stability) are thosein which Z has the formulae: ##STR17## wherein j preferably equals 1.These preferred end caps are conveniently prepared from relativelyinexpensive starting materials. Recent work also indicates that an endcap radical of the formula: ##STR18## wherein R₂ = ##STR19## is apreferred compound.

The polyetherimide oligomers of the present invention can be prepared byseveral reaction schemes. One such method comprises the simultaneouscondensation of: ##STR20## in the ratio of I:II:III:IV=1:1:m:m, whereinm is an integer greater than or equal to one. The product has thegeneral formula previously described. The reaction occurs in a suitablesolvent under an inert atmosphere. If necessary, the reaction mixturecan be heated to facilitate the reaction. The reaction conditions aregenerally comparable to those described in U.S. Pat. Nos. 3,847,869 and4,107,147, which are incorporated by reference.

Preferably the oligomer products possess thermoplastic properties, and,accordingly, have an average formula weight of between about5,000-40,000, and generally 20,000-30,000.

Alternatively, the polyetherimides can be prepared by reacting apolyetherimide polymer made by the self-condensation of a phthalimidesalt of the formula: ##STR21## with crosslinking end cap moieties of theformulae: ##STR22## wherein X=--O-- or --S--; ##STR23## n=1 or 2;##STR24## E=allyl or methallyl; Y=halo- or nitro-;

R₁ =any of lower alkyl, lower alkoxy, aryl, or substituted aryl;

R'=a divalent C.sub.(6-30) aromatic organic radical;

j=0, 1, or 2;

G=--CH₂ --, --O--, --S--, or SO₂ --; and

M=an alkali metal ion or ammonium salt or hydrogen.

The self-condensation proceeds as described in U.S. Pat. No. 4,297,474in a dipolar aprotic solvent. The end cap moieties can be introducedduring the self-condensation to quench the polymerization, or they mightbe added following completion of the polymerization and recovery of thepolyetherimide polymer from methanol. Improved solvent resistance on thecured composites is best achieved, however, by the quenching sequencerather than by the post-polymerization capping sequence.

Yet another preferred method for synthesizing the polyetherimides of thepresent invention involves the simultaneous condensation of about 2 m+2moles of nitrophthalic anhydride with about m+1 moles of diamine, aboutm moles of dialcohol, and 2 moles of A-OH in a suitable solvent under aninert atmosphere. Here, the dialcohol (hereinafter referred to also as adiol or a dihydric phenol) may actually be in the form of a phenate.

In this reaction, the diamines (which have, preferably, aromaticethersulfone backbones) react with the anhydride to form intermediatesof the following nature in the backbone: ##STR25## wherein R₂ =a residueof the diamine. Similarly, the dialcohol reacts with thenitro-functionality to form an ether linkage of the general formula:##STR26## wherein R₃ =a residue of the dialcohol. The A-OH end capsquench the polymerization. The resulting polyetherimides have thegeneral formula: ##STR27##

Yet another preferred synthesis comprises the simultaneous condensationof about 2 m+2 moles of nitrophthalic anhydride with about m+1 moles ofdialcohol, m moles of diamine, and 2 moles A-NH₂ in a suitable solventunder an inert atmosphere. Again, the dialcohol may be in the phenateform. The resulting oligomer has a general formula: ##STR28##

Yet another preferred synthesis comprises the simultaneous condensationof 2 m moles of nitrophthalic anhydride with about m+1 moles ofdialcohol, m moles of diamine, and 2 moles of A-NO₂ (a nitro-terminatedend cap) in a suitable solvent under an inert atmosphere. Again, thedialcohol may be in the phenate form or a corresponding sulfhydryl canbe used to form a thioether. The resulting oligomer has the generalformula: ##STR29##

In any of the syntheses, the dialcohol can be replaced by a comparabledisulfhydryl of the formula: HS-R₂ -SH. Mixtures of dialcohols, ordisulfhydryls, or of dialcohols and disulfhydryls can be used.

Suitable diamines are selected from the group consisting of: ##STR30##q=--SO₂ --, --CO--, --S--, or --(CF₃)₂ C--, and preferably --SO₂ -- or--CO--,

Me=CH₃₋₋ ;

m=an integer, generally less than 5, and preferably 0 or 1;

D=any of --CO--, --SO₂ --, or --(CF₃)₂ C--,; and

X=halogen.

Other diamines that may be used, but that are not preferred, includethose described in U.S. Pat. Nos. 4,504,632 and 4,058,505 (which areincorporated by reference). The aryl or polyaryl "sulfone" diaminespreviously described are preferred, since these diamines provide highthermal stability to the resulting oligomers and composites. Mixtures ofdiamines might be used.

The dialcohol is generally a polyaryl compound and preferably isselected from the group consisting of:

    HO--Ar--OH;

    HO--Ar--L--Ar'--L--Ar--OH;

    HO--Ar'--L--Ar--L--Ar'--OH;

wherein L=--CH₂ --, --(CH₃)₂ C--, --(CH₃)₂ C--, --O--, --S--, --SO₂ --or --CO--; ##STR31## T and T₁ =lower alkyl, lower alkoxy, aryl, aryloxy,substituted aryl, halogen, or mixtures thereof;

q=0-4;

K=0-3; and

j=0, 1, or 2;

hydroquinone;

bisphenol A;

a dialcohol having a Schiff base segment, the radical being selectedfrom the group consisting of: ##STR32## wherein R is selected from thegroup consisting of: phenyl;

biphenyl;

naphthyl; or

a radical of the general formula: ##STR33## wherein W=--CH₂ -- or --SO₂--; or a dialcohol selected from the group: ##STR34## wherein L is asdefined above; Me=CH₃ --;

m=an integer, generally less than 5, and preferably 0 or 1; and

D=any of --CO--, --SO₂ --, or --(CF₃)₂ C--.

While bisphenol A is preferred (because of cost and availability), theother dialcohols can be used to add rigidity to

the oligomer without significantly increasing the average formulaweight, and, therefore, can increase the solvent resistance. Random or ablock copolymers are possible.

Furthermore, the dialcohols may be selected from the dihydric phenolimide sulfone resins described in U.S. Pat. No. 4,584,364, which isincorporated by reference, or those dihydric phenols described in U.S.Pat. Nos. 3,262,914 or 4,611,048. In fact, the hydroxy-terminatedetherimides of U.S. Pat. No. 4,611,048 can be reacted with A-NO₂ toprovide crosslinking etherimides of the present invention.

Dialcohols of this nature are commercially available. Some may be easilysynthesized by reacting halide intermediates with bis-phenates, such asby the reaction of 4,4'-chlorophenylsulfone with bis(disodiumbiphenolate).

The oligomers can be synthesized in a homogeneous reaction schemewherein all the reactants are mixed at one time (and this scheme ispreferred), or in a stepwise reaction. The diamine and dialcohols can bemixed, for example, followed by addition of the nitrophthalic anhydrideto initiate the polymerization and thereafter the end caps to quench it.Those skilled in the art will recognize the variant methods that mightbe used. To the extent possible, undesirable competitive reactionsshould be minimized by controlling the reaction steps (i.e., addition ofreactants) and the reaction conditions.

Instead of Schiff base linkages in the dialcohols, these compounds mightinclude oxazole, thiazole, or imidazole linkages. All of these linkagespresent the potential for creating conductive or semiconductivecomposites, if suitably doped.

Dopants for creating semiconductive or conductive composites arepreferably selected from compounds commonly used to dope other polymers,namely (1) dispersions of alkali metals (for high activity) or (2)strong chemical oxidizers, particularly alkali perchlorates (for loweractivity). Arsenic compounds and elemental halogens, while activedopants, are too danagerous for general usage, and are not recommended.

The dopants react with the polymers to form charge transfer complexes.N-type semiconductors result from doping with alkali metal dispersions.P-type semiconductive result from doping with elemental iodine orperchlorates.

While research into conductive or semiconductive polymers has beenintense, the resulting compounds (mainly polyacetylenes, polyphenelenes,and polyvinylacetylenes) are unsatisfactory for aerospace applicatinsbecause the polymers are:

(a) unstable in air;

(b) unstable at high temperatures;

(c) brittle after doping;

(d) toxic because of the dopants; or

(e) intractable.

These problems may be overcome or significantly reduced with theconductive oligomers of the present invention.

While conventional theory holds that semiconductive polymers should have(1) low ionization potentials, (2) long conjugation lengths, and (3)planar backbones, there is an inherent trade-off between conductivityand toughness or processibility, if these constraints are followed. Toovercome the processing and toughness shortcomings common with Schiffbase, oxazole, imidazole, or thiazole oligomers, the oligomers of thepresent invention, include "sulfone" linkages interspersed along thebackbone providing a mechanical swivel for the rigid, conductivesegments of the arms.

Since it is difficult to include the oxazole, imidazole, or thiazolelinkages in the reactants, Schiff base compounds are preferred. Theprinciple focus of the invention is toward improved etherimide,thioetherimides, or sulfoneimides, and the conductive or semiconductivecomposites are not the preferred compounds of the present invention.They are but a small subset of the compounds that comprise the presentinvention.

Solubility of the oligomers becomes an increasing problem as the lengthof the backbones increases. Therefore, shorter backbones are preferred,so long as the resulting oligomers remain processible. That is, thebackbones should be long enough to keep the oligomers soluble thereaction sequence.

Blends of the crosslinkable oligomers and noncross-linking, compatiblepolymers can also be made. These blends generally comprise substantiallyequimolar mixtures of the oligomer and polymer. The polymer should havea backbone substantially identical with the oligomer, and may be made inaccordance with a process described in U.S. Pat. Nos. 4,297,474 or3,847,869.

Impact resistance of the cured composites formed from prepregs of theoligomers can be increased without deleterious loss of solventresistance by forming the prepregs with such a blend. Generally, theblend includes capped oligomers to provide crosslinking upon curing andnoncrosslinking polymers of a corresponding backbone to providecompatibility of the oligomer and polymer. A 50-50 blend on a molarbasis of oligomers and polymer may be formed by (a) dissolving thecapped oligomer in a suitable first solvent, (b) dissolving the uncappedpolymer in a separate portion of the same solvent or in a solventmiscible with the first solvent, (c) mixing the two solvent solutions toform a lacquer, and (d) applying the lacquer to fabric in a conventionalprepregging process.

Although the polymer in the blend usually has the same backbone(structure and formula weight) as the oligomer, the properties of thecomposite formed from the blend can be adjusted by altering the ratio offormula weight for the polymer and oligomer.

The terminal groups of the polymer are unimportant so long as thepolymer's terminal groups do not react with or impede the crosslinkingof the oligomer end caps. Also, it is probably nonessential that theoligomer and polymer have identical repeating units (structure), butthat the oligomer and polymer merely be compatible in the solution priorto sweeping out as a prepreg. Of course, if the polymer and oligomerhave identical backbones, compatibility in the blend is more likely.

The noncrosslinking polymer can be made by the same synthetic method asthe oligomer with the substitution of a quenching cap for thecrosslinking end cap. For example, phenol can replace end caps of theformula A-OH; aniline can replace end caps of the formula A-NH₂ ; and,nitrobenzene can replace end caps of the formula A-NO₂.

While the best blends are probably those in which the backbones areessentially identical and of modest formula weight and those in whichthe oligomer and polymer are in equimolar proportions, other variantblends may be prepared, as will be recognized by those of ordinary skillin the art.

Anhydrides of the formula: ##STR35## wherein X=--O-- or --S--; R=atrivalent C.sub.(6-13) aromatic organic radical; ##STR36## n=1 or 2;##STR37## R₁ =any of lower alkyl, lower alkoxy, aryl, or substitutedaryl; j=0, 1, or 2; and

G=--CH₂ --, --O--, --S--, or --SO₂ --,

are useful in the synthesis of the etherimides of the present invention,and are prepared by the condensation of the corresponding end cap phenolor thiol (-XH) with a nitro- or haloanhydride that contains the Rmoiety.

In at least one synthesis of the etherimides of the present invention, acompound of the formula: ##STR38## is an intermediate or reactant,wherein: R=a trivalent C.sub.(6-13) aromatic organic radical' ##STR39##n=1 or 2; ##STR40## E=allyl or methallyl; R₁ =any of lower alkyl, loweralkoxy, aryl, or substituted aryl;

j=0, 1, or 2; and

G=--CH₂ --, --O--, --S--, or --SO₂ --

This intermediate is formed by reacting A-NH₂ with a substitutedphthalic anhydride of the formula: ##STR41## wherein Y=halo- or nitro-.These substituted anhydrides are described in U.S. Pat. Nos. 4,297,474and 3,847,869.

Polysulfoneimide oligomers can be prepared by reacting about m+1 molesof a dianhydride with about m moles of a diamine and about 2 moles of anamine end cap (A-NH₂). The resulting oligomer has the general formula:##STR42## wherein R and R' are divalent aromatic organic radicals havingfrom 2-20 carbon atoms. R and R' may include halogenated aromaticC(6-20) hydrocarbon derivatives; alkylene radicals and cycloalkyleneradicals having from 2-20 carbon atoms; C.sub.(2-8) alkylene terminatedpolydiorganosiloxanes; and radicals of the formula: ##STR43## whereinq=--C_(y) H_(2y) --, --CO--, --SO₂ --, --O--, or --S--; and

y=1 to 5.

Comparable polymers, usable in blends of the sulfoneimides, aredescribed in U.S. Pat. No. 4,107,147, which is incorporated byreference. Other aromatic dithio dianhydrides are described in U.S. Pat.No. 3,933,862.

The oligomers of the present invention can be combined with reinforcingmaterials, such as fibers, chopped fibers, whiskers, or fabrics, andcured to composite materials using heat or chemicals to activatecrosslinking between end caps. Prepregs can be prepared by conventionalprepregging techniques. Curing generally is conducted in conventionalvacuum bagging techniques at elevated temperatures. The curingtemperature varies with the choice of end cap. If desired, mixtures ofend caps might be used.

While para--isomerism has generally been described, other isomers may beused. The phenyl or aryl moieties in the backbones can also includesubstituents so long as the substituents do not interfere with thecrosslinking or synthesis. While polyaryl compounds are described,aliphatic moieties can be included in the backbones, in some cases,although the ultimate use temperatures of these oligomers or compositesmay be lower than with entirely polyaryl backbones.

While preferred embodiments have been described, those skilled in theart will readily recognize alterations, variations, or modificationswhich might be made to the embodiments without departing from theinventive concept. Therefore, the claims should be interpreted liberallywith the support of the full range of equivalents known to those ofordinary skill based upon this description. The claims should be limitedonly as is necessary in view of the pertinent prior art.

We claim:
 1. A polyetherimide oligomer, comprising at least one productof the process of reacting: ##STR44## in about the stoichiometric ratioof I:II:III:IV=1:1:m:m, wherein m is an integer greater than or equal toone, the reaction product having the general formula: ##STR45## whereinX is --O-- or --S--; ##STR46## n is 1 or 2; ##STR47## E is allyl ormethallyl; Y is halo- or nitro-;R is a trivalent C.sub.(6-13) aromaticorganic radical; R₁ is a composition compression at least one of loweralkyl, lower alkoxy, aryl, or substituted R' is a divalent C.sub.(6-30)aromatic organic radical; j is 0, 1, or 2; and G is --CH₂ --, --O--,--S--, or --SO₂ --.
 2. A prepreg comprising a suitable reinforcement andthe oligomer of claim
 1. 3. A cured composite formed by curing theprepreg of claim
 2. 4. A cured composite formed by curing the oligomerof claim
 1. 5. A method of synthesizing a polyetherimide oligomer,comprising the step of reacting: ##STR48## is about the ratio of aboutI:II:III:IV=1:1:m:m, wherein m is an integer greater than or equal toone, the reaction product having the general formula: ##STR49## whereinR is a trivalent C.sub.(6-13) aromatic organic radical; X is --O-- or--S--; ##STR50## n is 1 or 2; ##STR51## E is allyl or methallyl; Y ishalo- or nitro-;R₁ is any of lower alkyl, lower alkoxy, aryl, orsubstituted aryl; R' is a divalent C.sub.(6-30) aromatic organicradical; j is 0, 1, or 2; and G is --CH₂ --, --O--, --S--, or --SO₂--,the reaction occuring in a suitable solvent under an inertatmosphere.
 6. A polyetherimide oligomer of the general formula:##STR52## wherein X is --O-- or --S--; ##STR53## n is 1 or 2; ##STR54##Me is methyl; E is allyl or methallyl;Y is halo- or nitro-; R₂ is atrivalent C.sub.(6-13) aromatic organic radical; R₁ is any of loweralkyl, lower alkoxy, aryl, or substituted aryl; R' is a divalentC.sub.(6-30) aromatic organic radical; j is 0, 1, or 2; and G is --CH₂--, --O--, --S--, or --SO₂ --.
 7. The oligomer of claim 1 wherein n is2.
 8. The oligomer of claim 1 wherein X is --O--.
 9. The oligomer ofclaim 7 wherein X is --O--.
 10. The oligomer of claim 1 wherein R isphenyl.
 11. The oligomer of claim 7 wherein R is phenyl.
 12. Theoligomer of claim 1 wherein j is 1 and R₁ =methyl or phenyl.
 13. Theoligomer of claim 1 wherein Z is ##STR55##
 14. The oligomer of claim 6wherein R is phenyl.
 15. The oligomer of claim 6 wherein n is
 2. 16. Theoligomer of claim 14 wherein n is
 2. 17. The oligomer of claim 14wherein R' is phenyl.
 18. The oligomer of claim 17 wherein m is 1 and Xis --O--.
 19. The oligomer of claim 17 wherein n is 2; X is --O--;Z is##STR56## j is 1 or 2; R₁ is methyl or phenyl; and G is --O-- or --CH₂--.